1. Field of the Invention
The present invention relates generally to an intercooler for a supercharged internal combustion engine and more specifically to a self-contained intercooler wherein coolant is evaporated under reduced pressure in a manner to utilize the latent heat of vaporization thereof and the vapor used as a vehicle for removing heat from the intercooler.
2. Description of the Prior Art
In order to improve engine performance superchargers especially exhaust gas driven turbo-chargers are often fitted to internal combustion engines. However, these devices, while improving engine performance, have encountered drawbacks in that the temperature of the air charged into the cylinders increases due to compression (often as high as 150.degree.-170.degree. C.) which reduces the density of the air thus reducing charging efficiency, and tends to induce knocking (in Otto cycle engines). To solve the latter mentioned problem it is usual to retard the ignition timing and/or lower the compression ratio. This of course also tends to reduce engine power output. Accordingly, it has been proposed to interpose an intercooler between the supercharging compressor and the engine cylinders in order to reduce the temperature of the incoming charge.
FIG. 1 shows an example of a previously proposed intercooler arrangement. This arrangement is integrated with the engine cooling system. In this arrangement coolant from a reservoir 1 is fed to a heat exchanger 2 which forms a vital part of the intercooler 3 and to a pressure pump or compressor 4. The pressurized fluid discharged by the pump 4 is circulated through the engine coolant jacket 5 to absorb the heat produced by the engine. The resulting high pressure-temperature mixture of boiling coolant and vapor is ejected toward a condenser through a variable nozzle jet pump 7. Simultaneously, the liquid coolant fed into the intercooler heat exchanger 2 absorbs heat from the supercharged air passing through the intercooler 3 and vaporizes. This vapor is extracted from the heat exchanger and directed to the condenser 6 under the influence of the venturi action produced by the ejection of the high temperature-pressure liquid/vapor mixture ejected from the variable nozzle jet pump 7. The vaporized coolant is condensed in the condenser 6 and returned to the reservoir 1.
However, this arrangement has encountered several drawbacks in that the compressor 4 consumes valuable engine output, in that it is very difficult to control the temperatures in the system to desired levels with any degree of reliability and in that the liquid coolant fed to the intercooler heat exchanger sometimes becomes excessively heated forming a superheated vapor which lowers the heat exchange efficiency of the intercooler. Further, upon stopping the engine the condensation of the vaporized coolant in the system induces a sub-atmospheric pressure therein which tends to induct air into the system. The system once contaminated with air tends to lose its efficiency due to the pockets and bubbles of air which can absorb little or no heat and which inevitably find their way into the condenser of the system. For further disclosure relating to this device, reference may be had to "MOTOR TREND" published in the U.S. in June 1983 and/or to Japanese Patent Application First Provisional Publication No. Sho 56-146417 (1981).
FIG. 2 shows a second example of a previously proposed intercooler disclosed in Japanese Patent Application First Provisional Publication No. Sho 57-46016 laid open to public inspection on Mar. 16, 1982. In this arrangement liquid coolant from the engine radiator is admitted to a heat exchanging device 9 via a valve 10. This valve is controlled by a level sensor 11 in a manner to maintain an essentially constant level of liquid coolant within the device. The hot supercharged air from the turbo-charger compressor C, passes over and around a plurality of essentially vertically arranged pipes or conduits 12 containing liquid coolant. A vacuum pump or the like 13 driven by an electric motor 14 (or alternatively by way of a mechanical connection with the engine crankshaft) is used to reduce the pressure within the liquid filled portion of the heat exchanger 9 to a level whereat the coolant boils at a suitably low temperature. The coolant vapor extracted from the heat exchanger by the pump 13 is discharged into the conduit 15 leading from the engine coolant jacket 16 to the engine radiator 8 and permitted to mix with the liquid coolant and condense at essentially atmospheric pressure.
However, this arrangement has suffered from the drawbacks that the vacuum pump 13 is relatively large and bulky consuming valuable engine room space as well as engine power and in that temperature control with respect to change in the temperature of the air discharged by the turbocharger tends to be undesirably sluggish.